Why do departments use both trunking and conventional
- Thread starter daggit
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Two reasons agencies use both digital trunked systems and analog frequencies:
Backup system if the digital trunked system fails.
Analog tone pagers are still commonly used to alert personnel.
Programming both is a good idea.
Backup system if the digital trunked system fails.
Analog tone pagers are still commonly used to alert personnel.
Programming both is a good idea.
Whether it is necessary depends on the agency. Sometimes for a while after switching to a trunked system, an agency will keep their old conventional channels for a while. Sometimes they will repurpose them to other uses.
We have a couple of agencies down here that are on trunked systems yet maintain conventional channels for various reasons. Some of those conventional channels are used as additional police tac channels (which can also be used in case of system failures). One of the fire departments uses their old UHF frequencies for paging and vehicle tracking. And then there's Miami-Dade Fire which operates mostly on their UHF system except when communicating with any of our trauma centers, at which point they use the Miami-Dade P25 trunked system. So yes, definitely worth programming both types.
Cumberland Co and Fayetteville to include local Police Depts. have completely done away with old systems and radios, also have noticed that the Highway Patrol B Trp have stopped the use of 42.50 MHz, North Carolina
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bb911
Member
RR states this for the trunked system of San Bernardino County, CA: "The [following] system of conventional 800 MHz repeaters is used to fill in gaps in coverage of the countywide trunked systems."
San Bernardino Co. is the largest county in the US in area, the vast majority of it being desert which is full of peaks and valleys. (If you're wondering about Alaska -- it is divided into 19 organized boroughs and one "Unorganized Borough".-- per Wikipedia).
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RKG
Member
Conventional channels are also used where the ability to use "direct" (i.e., mobile or portable transmitting on repeater output freq) is important. For instance, this is the reason why NFPA 1221 "outlaws" use of a trunked talkgroup on the fireground.
Project25_MASTR
Millennial Graying OBT Guy
There a many reasons. Often times, it has to do with redundancy. Many public safety systems are airtime systems, meaning those who don't own infrastructure on the system often have to pay to play...or in other words it costs them a monthly fee per radio on the system and as such, non-primary services utilize conventional systems. Very few volunteer departments utilize trunking due to the cost of the subscribers and those that do typically maintain analog paging due to the low cost of analog pagers.
davidzimmerman
Member
Here in Cleveland Ohio SOME Fire Departments are on a P25 System and have Analog Fire Grounds on 700\800MHZ Frequencys
Expanding a little on RKG's comment. . .
Trunked systems are "guaranteed/designed/presumed" to have 95% coverage, meaning there is 5% that may be in "dead spots". These conventional frequencies are usually simplex/direct so that responders in the "dead spots" will have communications with each other. It's rather lonely to be in a basement that is out of range of your system and a crisis to occur.
Another term for these channels would be "Scene of Action" channels.
Trunked systems are "guaranteed/designed/presumed" to have 95% coverage, meaning there is 5% that may be in "dead spots". These conventional frequencies are usually simplex/direct so that responders in the "dead spots" will have communications with each other. It's rather lonely to be in a basement that is out of range of your system and a crisis to occur.
Another term for these channels would be "Scene of Action" channels.
Project25_MASTR
Millennial Graying OBT Guy
That’s pretty far off. They are built to cover the most the budget will allow typically with the highest amount of reliability. That’s why it’s something that typically goes out for bid. Assuming a system was designed for 95% percent coverage without knowing what was quoted and what was actually signed off on…is something that gets people killed.
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I don't think so, but will acknowledge there are always exceptions.
The nationally recognized standard for Emergency Services Communications Systems says: "9.3.1.2.1 Radio communication systems shall be designed to provide no less than 95 percent coverage of the jurisdictional area . . . "
Around our part of the world we got a new system some 6 years ago and we didn't have that 95% coverage, so the city fathers installed an additional site. Guess we are blessed!
The nationally recognized standard for Emergency Services Communications Systems says: "9.3.1.2.1 Radio communication systems shall be designed to provide no less than 95 percent coverage of the jurisdictional area . . . "
Around our part of the world we got a new system some 6 years ago and we didn't have that 95% coverage, so the city fathers installed an additional site. Guess we are blessed!
A couple of fire departments in south eastern VA have both a trunked system and their old conventional channels. York County simulcasts dispatches on both the trunked and old VHF channel.
Numerous other good reasons were listed previously.
Numerous other good reasons were listed previously.
Project25_MASTR
Millennial Graying OBT Guy
Jurisdictional area to the primary department/municipality building the system. Doesn't include neighboring municipalities which hopped on long ago or situations where additional areas have been annexed. You fail to recognize that not all systems are utilized solely by those who built them, especially when you get into multi-site, wide-area systems.
mmckenna
I ♥ Ø
That's from NFPA 1211.
Adoption of that standard varies from area to area. It can be hard for a fire marshal to force a PD or Sheriff department to adopt the NFPA standards intended for fire services.
But it would be nice if they did. It's a pretty good standard to shoot for.
I'll also add that The nice thing about standards is that there are so many to choose from.
I agree - this standard probably doesn't have many jurisdictions that "legally adopt" it for enforcement purposes. Most likely jurisdictions will refer to it as part of their bid process for radio systems or serve as a good guide for how things should be done.
At least for the fire service end, the real "enforcement" of this standard isn't by a fire marshal. Rather it's the Insurance Services Office that assigns ratings to fire departments. One of the many things they look at is handling of alarms and compliance with NFPA 1221.
Mcore25 - My point is that trunked radio systems have dead spots and conventional channels are used in those dead spots. Also if for whatever reason good or bad, an agency chooses to not use the system, rather go with simplex communications for scene communications. That's why departments may hang on to their conventional channels even when a trunked system is involved, which is what the OP was asking about.
At least for the fire service end, the real "enforcement" of this standard isn't by a fire marshal. Rather it's the Insurance Services Office that assigns ratings to fire departments. One of the many things they look at is handling of alarms and compliance with NFPA 1221.
Mcore25 - My point is that trunked radio systems have dead spots and conventional channels are used in those dead spots. Also if for whatever reason good or bad, an agency chooses to not use the system, rather go with simplex communications for scene communications. That's why departments may hang on to their conventional channels even when a trunked system is involved, which is what the OP was asking about.
MysterAitch
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At the risk of overthinking it, how is the 95% typically calculated? The quote above suggests it's 95% of land/water surface area (as opposed to population or some other metric).
If a signal can be gained while stood on the roof of a building stood but not within the ground floor or basement areas of the same building, does that building's footprint "count" toward the 95% of "jurisdictional area"?
How about other dense urban/high-rise areas such as NYC where reflection/penetration can be an issue therefore the area where signal can be deemed "usable" will be somewhat patchy?
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Project25_MASTR
Millennial Graying OBT Guy
I believe NFPA currently defines coverage as a -95 dBm signal or stronger. In a building it would be the same definition (and meeting some of that often takes BDAs if following NFPA guidelines).
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mmckenna
I ♥ Ø
NFPA 1221:
9.3.1.3.1 Radio communications systems shall be designed to provide no less than 95 percent coverage of the jurisdictional area, 95 percent of the time, with a 95 percent confidence factor.
9.3.1.3.2.1 Outdoors, a minimum of -107dBm to and from a portable radio worn on the hip shall be required.
9.3.1.3.2.2 For special structures and high rise buildings, a minimum of -95dBm to and from a portable radio worn on the hip shall be required
9.3.1.3.2.3 For all other structures that are capable of being occupied by persons on a regular basis, a minimum of -107dBm to and from a portable radio worn on the hip shall be required
9.3.1.3.1 Radio communications systems shall be designed to provide no less than 95 percent coverage of the jurisdictional area, 95 percent of the time, with a 95 percent confidence factor.
9.3.1.3.2.1 Outdoors, a minimum of -107dBm to and from a portable radio worn on the hip shall be required.
9.3.1.3.2.2 For special structures and high rise buildings, a minimum of -95dBm to and from a portable radio worn on the hip shall be required
9.3.1.3.2.3 For all other structures that are capable of being occupied by persons on a regular basis, a minimum of -107dBm to and from a portable radio worn on the hip shall be required
mmckenna
I ♥ Ø
95% fits in there a lot.
Especially the "with a 95 percent confidence factor", which translates into "I'm 95 percent sure I'm right in my calculations that the system will meet these requirements.
Or, if you will
There's a 5% chance that it's not going to work.
Especially the "with a 95 percent confidence factor", which translates into "I'm 95 percent sure I'm right in my calculations that the system will meet these requirements.
Or, if you will
There's a 5% chance that it's not going to work.
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